The present invention relates to a method of and apparatus for transporting earthy material containing water, especially mud or like material at the bottom of bodies of water, in a high concentration of the material and continuously to a prescribed site for disposal.
In recent years, it has been increasingly widely operated to transport earthy material deposited on the bottom of a dam, harbor or river to the prescribed site for disposal of the material. In order to dredge and transport the material deposited on the water bottom efficiently to the site for disposal, it is necessary to reduce the content of water in the material-water mixtures as much as possible and transport the mixtures continuously to the site while a high concentration of the material is maintained.
A variety of methods for dredging and transporting earthy material at the water bottom have been proposed, as exemplified by U.S. Pat. Nos. 2,346,180 and 3,842,521.
In each of these methods, the mud or like material deposited at the bottom of bodies of water is sucked by a nozzle or agitated to increase its fluidity so that it may be sucked and pressurized for transportation.
The problem encountered in case where mixtures of soil and water are to be sucked will be described in the following. Since solids in the mixture are sucked through an inlet port of a pump along the flow of solid-water mixture, in case the mixture has a fluidity near that of water, it is possible to transport the mixture by pumping as in transporting water alone. However, in case the fluidity is relatively low, soil or solids and water can hardly form a homogeneous mixture and there becomes a water channel formed in the mixture, whereby it tends to occur that water is transported in a greater amount than the soil or solids, resulting in that soil or solids are hardly transported.
Therefore, in the art of dredging, important are how to suppress the content of water in mixtures to be dredged and how to continuously transport dredged mixture. The inventor of the present invention has before developed such apparatus by which mud deposited on a water bottom is dredged in a high density or concentration and transported with the content of water suppressed as small as possible, and has proposed the apparatus in Japanese patent application Kokai publication No. 63-134721.
This apparatus is constructed as shown in FIG. 11, and comprises an annular cutter wheel 2 (or bucket wheel) fitted and rotated around a mud tank 1.
In the cutter wheel 2, an axle 3 extending in the center is borne by a bearing 4 with respect to the mud tank 1 so that a pulley 5 fixed at one end of the axle 3 may be driven through a belt 6 by a drive source 7. The cutter wheel 2 is equipped with buckets 8 which project at a spacing from a cylindrical body 2a thereof. The bucket 8 is formed in its bottom with an opening 9 which extends in the body 2a along the bucket 8, so that mud M excavated by the bucket 8 from the water bottom may be poured into the mud tank 1 from an opening 10 formed in an upper portion of the tank 1.
The axle 3 extending in the center of the mud tank 1 is further equipped with an agitating vane 11 for agitating and fluidizing the mud M poured through the opening 10. The mud tank 1 has its upper half portion covered with a hood 12 which is formed at its top with an air supply port 13 and at its skirt with an air release port as indicated at 13a in FIG. 2.
The mud tank 1 is further equipped at its bottom with a connection pipe 14, through which the mud M is conveyed so that it is pressurized by a pressurizing vane 15 and supplied to a pneumatic pump 16.
This pneumatic pump 16 is composed of such as a stop valve 19 for closing a discharge port 18 of a casing 17 accommodating the aforementioned pressurizing vane 15, a mud pipe 21 equipped with a check valve 22, and a pressurized air supply pipe 20.
The pneumatic pump 16 is usually made of three sets which are operative to supply and transport the mud alternately. During the mud transportation, specifically, the air under pressure left in one pneumatic pump 16 is discharged from the pressurized air supply pipe 20, and the mud M in the mud tank 1 is then pressurized by the pressurizing vane 16 and supplied to the pneumatic pump 16. Then, the stop valve 19 is closed, and the air under pressure is supplied from its supply pipe 20 and transported from the mud pipe 21. These steps are alternately accomplished by those three sets of pneumatic pumps.
Since the mud pipe 21 is equipped with the check valve 22, its pressurized air is prevented from flowing back into the pneumatic pump 16 when the air under pressure is to be discharged from the pneumatic pump 16.
However, the mud transporting method using the pneumatic pump 16 is accompanied by the following problems.
(1) In case the mud is to be pumped by using the pneumatic pump, compressed air under high pressure is supplied to the inside of the pump containing the mud, so that the mud may be pneumatically pumped. When the pump is then supplied with the mud, the compressed air has to be discharged at the mud supply step from the pump inside so that serious noises are generated.
(2) In case the mud is to be pumped by using the pneumatic pump, a series of operations of the mud supply to the pneumatic pump--the pressurization by the compressed air--the mud supply are required to use one group of pneumatic pumps. The supply and discharge of the mud to those pumps have to be accomplished intermittently. This makes the mud transportation intermittent with a low efficiency to enlarge the size of the apparatus.